Night vision systems include image intensification, thermal imaging, and fusion monoculars, binoculars, and goggles, whether hand-held, weapon mounted, or helmet mounted. Conventional night vision systems are typically equipped with one or more image intensifier tubes to allow an operator to see visible wavelengths of radiation. The systems work by collecting the tiny amounts of light, including the lower portion of the infrared (IR) light spectrum, that are present but may be imperceptible to human eyes, and amplifying it to the point that an operator can easily observe the image. These devices have been used by soldier and law enforcement is personnel to see in low light conditions, for example, at night or in darkened buildings. These devices take ambient light, magnify the light and display the image for viewing through an eyepiece. A drawback of night vision goggles is that they cannot see through smoke and heavy sand storms and cannot see a person hidden under camouflage.
Infrared thermal sensors allow an operator to see people and objects because they emit thermal energy. These devices operate by capturing the upper portion of the infrared light spectrum, which is emitted as heat by objects instead of simply reflected as light. Hotter objects, such as warm bodies, emit more of this wavelength than cooler objects, like trees or buildings. Since the primary source of infrared radiation is heat or thermal radiation, any object that has a temperature radiates in the infrared region.
Fusion systems have been developed that combine image intensification with thermal sensing. The image intensification information and the infrared information are fused together to provide a fused image that benefits over just image intensification or just thermal sensing. Whereas typical night vision devices with image intensification can only see visible wavelengths of radiation, the fused system provides additional information by providing heat information to the operator.
Fusion sensor systems attempt to show two images on top of each other. In the case of image intensified (I2) cameras and thermal (LWIR) cameras, they tend to show the I2 image in a green color (bright green=many photons; black=few photons) and the LWIR image in a warm color-like amber (very hot=bright amber; very cold=black).
Both sensors compete for visual space on every pixel of the display. This may create a cluttered image and a viewer may not be able to distinguish important details in one of the sensors, because it is drowned out by the visual information of the other sensor. One method of dealing with this clutter includes an overlay mode, which shows all of the I2 imagery but only the LWIR imagery above a predetermined threshold temperature. This, however, still has the problem of cluttering in the hot regions. Thus, fusion systems are frequently cluttered due to attempts to put data from two sensors into one image space.
As will be explained, the present invention improves the viewability of an I2 image and a thermal image which have been fused, or combined on a single display in a night vision device.